The present invention is related to Japanese patent application No. 2000-234087, filed Aug. 2, 2000; the contents of which are incorporated herein by reference.
The present invention relates to a method of fabricating brushes, and more particularly to a method of manufacturing brushes which slide in contact with the surface of a commutator of an armature.
There has been a known method of adopting a brush of double-layer construction as a means to improve commutator characteristics and accordingly to prolong brush life. The double-layer brush is a laminate formed for example of a first brush material (low carbon) of high resistivity and a second brush material (high carbon) of low resistivity. Good brush characteristics are obtainable by arranging particularly the second brush material orthogonally to the direction of rotation of the commutator and also by using a thin material of uniform thickness.
When the double-layer brush is used in an armature (shown in FIG. 7) having a surface-type commutator (the commutator surface is orthogonal to the axis of rotation), the shape of the end face of the brush in sliding contact with the commutator surface is preferably shaped as each segment constituting the commutator. For example, as shown in FIG. 5, when each segment is inclined to the direction of rotation (not along the radial direction), the end face of the brush becomes irregular, approximately trapezoidal in shape (a shape projected on the commutator surface) which is inclined in relation to the direction of rotation, correspondingly to the shape of the segment.
To mold the uniform, thin second brush material in fabricating the double-layer brush of irregular shape, it is necessary to press and mold the brush powder of the second brush material in a level state. In the conventional practice, as shown in FIG. 8, a molding die equipped with a lower punch 200 and an upper punch 210, which slides up and down, is used to mold the second brush material in a level position, thereby pre-molding a rectangular brush block 100A. After molding, an unnecessary portion is removed by cutting or other means, to make a double-layer brush having an irregular shape.
The conventional method of fabrication shown in FIG. 8, however, presents such a problem that, because removal of the unnecessary portion from the brush block 100A is needed, material yields become very low, resulting in a high unit price of products. Furthermore, a process is needed to remove the unnecessary portion from the brush block 100A. Therefore, not only does the number of fabricating processes increase, but an enormous facility cost is required. Furthermore, a tool mark remains on the sliding surface of the brush when the unnecessary portion is removed, resulting in deteriorated sliding performance of the brush.
In view of the above-described circumstances, it is an object of the invention to provide a method of fabricating brushes to be used in an armature having a surface-type commutator. More specifically, it is an object of the invention to provide a method for easily fabricating brushes of multi-layer construction for use correspondingly to the shape of segments constituting the commutator.
In a first aspect, brushes are configured with the projected form of their plane on the surface of the commutator conforming to the shape of the segments, and are each formed by laminating a first brush material produced from a first brush powder on a second brush material produced from a second brush powder. The first brush material is placed on the front side in the direction of rotation of the armature, and the second brush material on the rear side. The second brush material is set at nearly fixed values in thickness. The front end face of the first brush material is inclined to a predetermined angle in relation to the rear end face of the second brush material. The brushes are fabricated through the following molding process.
The molding process includes the first molding process in which the first brush powder is charged onto the pressure receiving face of the lower punch and then the upper punch is fed down to press to form the first brush material, and the second molding process in which, after the upper punch is raised, the second brush powder is charged onto the first brush material thus molded and the upper punch is fed down again to press to form the second brush material.
In the molding die used in the brush fabricating process, the pressure applying face of the upper punch is formed nearly level, and the pressure receiving face of the lower punch is inclined at a predetermined angle in relation to the pressure applying face of the upper punch (the angle of inclination of the front end face of the first brush material in relation to the rear end face of the second brush material). Therefore, in the first molding process, the first brush material can be molded into a predetermined shape, and the upper surface of the first brush material which serves as an interfacial boundary with respect to the second brush material can be molded nearly level. In the second molding process, therefore, since the second brush powder can be charged onto the nearly level surface (the upper surface of the first brush material), it is possible to uniformly press the second brush powder to produce the second brush material of nearly uniform, fixed thickness.
In another aspect, the plane form to be projected on the commutator surface of the brush corresponds to the shape of the segment. Therefore, the brush is made of the first brush material molded of the first brush powder laid on the second brush material molded of the second brush powder. The first brush material is arranged on the front side in the direction of rotation of the armature, and the second brush material on the rear side. The second brush material has nearly fixed thickness, and the front end face of the first brush material is inclined to a predetermined angle in relation to the rear end face of the second brush material.
The brush is fabricated through the following molding process. The molding process includes the first molding process in which the second brush powder is charged onto the pressure receiving face of the lower punch, the first upper punch is fed down to press to mold the second brush material, and the second molding process in which, after the first punch is elevated, the first brush powder is charged onto the second brush material thus molded, then the second upper punch is fed down to press to mold the first brush material.
In the molding die used in the brush fabricating process, the pressure receiving face of the lower punch and the pressure applying face of the upper punch are each formed nearly level. Therefore, in the first molding process the second brush powder can be charged onto the nearly level surface (the pressure receiving face of the lower punch). Therefore, it is possible to apply a uniform pressure to the second brush powder with the first upper punch, to thereby uniformly form the second brush material having approximately fixed thickness.
Furthermore, since the pressure applying face of the second upper punch is inclined to a predetermined angle to the pressure receiving face of the lower punch (the angle of inclination of the front end face of the first brush material in relation to the rear end face of the second brush material), the first brush material can be molded to a predetermined shape in the second molding process.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.